How can i make a brick become unanchored if a player touches the brick not click?

Use the .Touched Event and change part's property Anchored to false.

Here's an example :

local Debounce = false

local Part = Instance.new("Part") --Making part
Part.Position = Vector3.new(0,5,0) --Setting position
Part.Anchored = true --Anchored to true so the part "float" in air
Part.Parent = game.Workspace --Parent to Workspace so the part become visible

Part.Touched:Connect(function(Hit) --When the part is touched then this function runs
   if Hit.Parent:IsA("Model") then --Checking if the parent of the object that touched our part is a model
      if Hit.Parent:FindFirstChild("Humanoid") then --Checking if the model have a humanoid , if yes then it's a player (or a npc)
         if not Debounce then --Using a debounce because the .Touched event fire every time the object that touched the part moves
            Part.Anchored = false --Setting Anchored to false so the part falls
            Debounce = true --Setting the debounce to true
         end
      end
    end
end)